Recently, a vehicle equips an air bag apparatus at front portion thereof (on a driver seat or on a passenger seat) for improving safety on a collision. When the vehicle crashes into an object due to an accident, the air bag apparatus outputs a signal (an operation signal) to an air bag actuator based on a signal from the collision detecting sensor for actuating an inflator and inflating the air bag instantaneously.
On this account, for improving the safety on the vehicle collision, a vehicle having a function for switching a place where the air bag is inflated considering a direction of the impact due to the vehicle collision has been on a market. In this case, the air bag needs to be actuated based on an accurate determination whether or not a passenger is sitting on the vehicle seat. The judge whether or not the passenger is sitting on the vehicle seat, especially on the passenger seat, needs to be done more precisely because such seat may be variously occupied by a adult, a children or a baby on a child seat (Child Restraint System, hereinafter referred to as CRS).
Various types of the occupant detecting devices for determining whether of not the passenger is sitting on the vehicle seat have been disclosed so far. For example, an occupant detecting device including plural cells at the seating surface thereof for detecting a partial pressure applied to a certain point of the vehicle seat where is defined by a matrix in a two-dimensional array of rows extending in a width direction of the vehicle seat and columns extending in a cross direction of the vehicle seat as disclosed in a Japanese Patent Laid-Open Publication No.2002-87132.
Such occupant detecting device tends to be affected by temperature, so that occupant detecting devices need to be able to correct such influences. For example, according to Japanese Patent Laid-Open Publications No.2001-4469, No.2000-28366 and No.2003-14564, temperature detecting element is embedded in a pressure sensor applied to the occupant detecting device, and sensitivity and a characteristic of the pressure sensor being affected by temperature can be corrected depending on the detected temperature by the element. Further, according to a Japanese Patent Laid-Open Publication No.2002-160571, an estimated weight obtained based on a sensor signal for determining the seat condition may be corrected. Specifically, based on a detected value of the temperature sensor, a characteristic curve is selected, and a correction factor for the weight estimation is determined.
In such known occupant detecting devices, the pressure detected by the pressure sensor is corrected in consideration of such characteristic of the pressure sensor being affected by temperature change; however, influences due to the temperature may differ when the occupant detecting device is actually embedded inside the vehicle seat. For example, when the occupant detecting device is embedded at a urethane pad in the vehicle seat, the pressure sensor may be affected by a hardness change of the urethane pad as well as the aforementioned characteristic of the pressure sensor being influenced from temperature change.
The known occupant detecting devices have not considered possible influences due to the temperature change on mounted condition in the vehicle seat, such as the influence of the hardness of the urethane pad and the like. The present invention therefore seeks to provide an occupant detecting device for improving the accuracy of determining a condition of the vehicle seat on mounted condition in the vehicle seat in spite of the effect of temperature.